1. Field of the Invention
The present invention pertains to a clutch disk, comprising a hub area and a plurality of friction lining elements, which are supported on the hub area and arranged in sequence around the circumference relative to a clutch disk rotational axis, these elements providing at least part of an associated friction surface area, where the friction lining elements are designed to make frictional contact with an associated opposing friction surface of a flywheel, pressure plate, or the like.
2. Description of the Related Art
In conventional clutch disks, the friction linings, either in the form of individual friction lining elements or ring-like friction linings, are usually attached rigidly to the hub area with rivets, for example. It is also known that the friction linings or individual elements thereof can be attached by way of so-called lining springs to the hub area, so that, when engaging and release operations are carried out, an axial elasticity within the clutch disk is obtained, which has a supportive effect especially during release operations. When, in friction clutches equipped with clutch disks of this type, local changes occur in the frictional conditions as a result of, for example, a local change in the coefficient of friction, a corresponding change occurs in the torque being transmitted by the clutch disk, even though no change is made in the position of the clutch by the release mechanism during the time that the clutch is slipping.
It is the task of the present invention to provide a clutch disk which can compensate for local changes in the frictional conditions while the clutch is slipping.
According to the invention, at least one friction lining element is designed so that the contact pressure of at least certain parts of its friction surface area against an opposing friction surface can change, at least in response to a change in the sliding frictional interaction between its friction surface area and the opposing friction area which is or can be associated with it.
The present invention takes advantage of the knowledge that the clutch torque MK transmitted by a friction clutch equipped with this type of clutch disk is a function of various physical variables such as the coefficient of friction xcexc, the normal force FN acting between the two surfaces rubbing against each other, the mean friction radius r of the friction surfaces, and the number z of pairs of friction surfaces which are rubbing against each another. This relationship is expressed by the following equation:
MK=xcexcxc2x7zxc2x7rxc2x7FN 
When now, for example, a change in the sliding frictional interaction occurs, such as that which may be caused by a change in the coefficient of friction at various points around the circumference, such a change, e.g., possibly an increase, can be compensated according to the invention by a change in the contact force exerted by at least one friction lining element or its friction surface area. Such a change in the contact force has the result that the normal force FN acting between the surfaces rubbing against each another decreases at certain points and thus, for example, an increase in the coefficient of friction xcexc is compensated by a decrease in the normal force FN.
The indicated change can be obtained by connecting the minimum of one friction lining element to the hub area by a support element, which is itself supported on one of the circumferential ends of the friction lining element. When there is a change in the sliding frictional interaction, a force is generated with the participation of the support element which tries to push at least certain parts of the friction lining element away from the opposing friction surface. For this purpose it can be provided, for example, that the part of the support element between the point where it is connected to the hub area and the point where it is connected to the minimum of one friction lining element curves in the axial direction toward the opposing friction surface which is or can be associated with it. To avoid excessive axial load on the support elements, it is proposed that two friction lining elements, the friction surface areas of which point essentially in opposite axial directions, are supported against each other. This can be realized, for example, in that the support elements of two friction lining elements with friction surface areas which point in different axial directions are supported against each other at the ends pointing away from the connection with the hub area.
An arrangement which in particular is equally effective in both directions of torque transmission, that is, in both directions of relative rotation, can be obtained by connecting at least one circumferential end of the support element to the hub area with freedom of movement in the axial. To avoid secondary bending while making this axial movement possible, it is proposed that at least one circumferential end of the support element be connected to the hub area with freedom of movement in the circumferential direction
Another possibility of providing for the axial displacement of a surface of at least one friction lining element, i.e., for a change in the contact force, consists in connecting the support element to the hub area in such a way that it can swivel and/or undergo elastic deformation in the area between its connection to the hub area and the friction lining element, and by offsetting the friction surface area axially relative to the connection between the support element and the hub area in the direction toward an opposing friction surface which is or can be associated with it.
It can also be provided that a plurality of friction lining elements arranged in sequence in the radial or circumferential direction is carried on the support element. The axial displacement of a friction lining element, i.e., of its surface area, can also be achieved by supporting the support element on the hub area by way of a sliding wedge device, so that it can shift position in the axial direction.
An especially simple design can be obtained by supporting the two support elements of two friction lining elements with friction surface areas facing in opposite axial directions elastically against each other, each one being pretensioned in the axial direction toward an opposing friction surface which is or can be associated with it, and by providing each support element with at least one wedge surface, which cooperates with an associated opposing wedge surface on the hub area in such a way that, at least when there is a change in the sliding frictional interaction with at least one of the two friction lining elements, at least certain areas of the support element of the one friction lining element can shift axially toward the support element of the other one of the two friction lining elements.
According to another embodiment which is especially easy to construct but very reliable and certain in its operation, the axial movement can be further enabled by supporting the minimum of one friction lining element on the hub area by way of an elastic support mass. For this purpose, it is possible for the minimum of one friction lining element to comprise a plurality of friction lining element parts, which extend away from the support element both axially and circumferentially, the axial ends of these parts forming at least part of the friction surface area, parts of the elastic support mass being provided between them.
According to another alternative embodiment, the minimum of one friction lining element can be provided with a plurality of projecting friction areas for frictional interaction. The preferred design in this case is for the minimum of one friction lining element to have a lining of friction material, on which a plurality of frictional projections are formed, which are arranged in sequence in the circumferential and/or radial direction. As an alternative, however, it is also possible for the minimum of one friction lining element to have a plurality of separately formed friction material elements arranged in sequence in the circumferential and/or radial direction. These friction material elements can be designed in the form of lips or bumps.
To prevent the normal force from falling below a certain minimum value, a device for limiting the movement in the axial direction can be provided. An axial stroke-limiting device such as this ensures that the axial displacements induced when the contact or normal force decreases cannot exceed a certain value, so that, regardless of the prevailing frictional relationships, a certain minimum normal force always remains in effect.
So that primarily local changes in the frictional relationships can be taken into account, it is proposed that the contact force of the minimum of one friction lining element or of a group of friction lining elements have the ability to change essentially independently of the other friction lining elements or groups of friction lining elements.
According to another aspect, the present invention pertains to a friction lining assembly for a friction clutch or the like, comprising at least one friction lining element with a plurality of projecting frictional areas designed for frictional interaction.
In this embodiment, it is also possible in particular to provide, for example, a continuous element in the form of a ring as the friction lining element. In this case, the area of the individual frictional projections is or can be deformable in order to obtain the previously described local differences in the interaction with the opposing friction surface.
The present invention also pertains to a friction clutch with a clutch disk according to the invention.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.